US Bridges

IRR - S 66 over Three Mile Coulee

FairPosted for load

Blaine County, Montana · 3M S Fort Belknap Agency · Structure no. P00066047+02171

Built
1959
66 years old
Condition
Fair
inspected June 2023
Type
Stringer/Multi-beam or Girder
Wood or Timber
Length
100 ft
4 main spans
Daily traffic
763
2023 count
Owner
State
State Highway Agency

About this bridge

IRR - S 66 over Three Mile Coulee is a wood or timber stringer/multi-beam or girder carrying IRR - S 66 over Three Mile Coulee in Blaine County, Montana. It was built in 1959, so it is 66 years old, older than the Montana average of 47 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 6 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. Its operating status is: posted for load restriction.

It carries about 763 vehicles a day, roughly 4% of them trucks, projected to reach 801 by 2043. The structure is 100 ft (30.5 m) long and 30 ft wide. If it were closed, the detour would be 87 mi (140 km).

Location

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CarriesIRR - S 66
CrossesThree Mile Coulee
Location3M S Fort Belknap Agency
RouteState Highway 66
CountyBlaine County
StateMontana
Coordinates48.44494, -108.74176
Functional classRural Minor Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionJune 2023
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating42 US tons
Inventory rating27 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialWood or Timber
DeckWood or timber
Main spans4
Design loadHS 15
Structure length100 ft (30.5 m)
Longest span25 ft (7.6 m)
Deck width30 ft (9.1 m)
Roadway width29 ft (8.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic763 (2023)
Projected traffic801 by 2043
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed87 mi (140 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was IRR - S 66 over Three Mile Coulee built?

It was built in 1959, making it 66 years old in 2025.

What condition is IRR - S 66 over Three Mile Coulee in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in June 2023.

How much traffic does IRR - S 66 over Three Mile Coulee carry?

About 763 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is IRR - S 66 over Three Mile Coulee?

The structure is 100 ft (30.5 m) long with a longest span of 25 ft (7.6 m) and a deck 30 ft wide.

Who owns IRR - S 66 over Three Mile Coulee?

It is owned by the State Highway Agency.